The present invention relates to a device for reading from and/or writing to recording media in disc form which has an unbalance compensation means.
A device of this type is disclosed in WO 84/01863. This device has a brushless DC motor as drive motor which causes the recording medium in disc form to effect a rotary movement. The recording medium is secured to the drive motor by means of a securing means, in this case the motor hub. In order to obtain a rotary movement of the recording medium which is as free as possible from unbalance, the DC motor, as the unbalance compensation means, is designed in such a way that milling has to be effected only once at one location in order to obtain unbalance compensation. The device is constructed in such a way that no unbalance can arise in the course of assembly, repair or the like.
The known device may be regarded as having the disadvantage that freedom from unbalance exists only when the recording medium in disc form also has no unbalance at all. Although this can be ensured in the case of hard disc devices, this is not so in the case of devices having exchangeable recording media.
The object of the invention is to propose a device of the abovementioned type which has the smallest possible unbalance even when exchangeable recording media are used.
This object is achieved by means of the measures specified in the independent claims.
The invention provides for the unbalance compensation means to be a centrifugal force generation means which generates a centrifugal force which is variable during operation. The advantage of such a dynamic unbalance compensation means consists in the fact that tolerances of the recording medium, tolerances in the securing thereof and also tolerances of the drive motor are permitted to be relatively high without the unbalance caused thereby having a disruptive influence on the operation of the device, since this unbalance is compensated for by the dynamic unbalance compensation means and is adapted to possibly changing conditions even during operation. Recording media afflicted by unbalance, such as so-called shape CDs, for example, which under certain circumstances do not have uniform mass distribution, can be played back without difficulty in a device according to the invention.
Another aspect of the present invention provides for the unbalance compensation means to be a positioning means for positioning the recording medium. This has the advantage that the unbalance is compensated for directly at its source. That proportion of the unbalance which is caused by the recording medium or the positioning thereof in the device and, by its nature, cannot be compensated for during the production or service of the device is thus compensated for. The positioning means serves to position the recording medium in such a way that the centre of mass of the said recording medium is oriented such that it is centred with respect to the axis of the drive motor or the axis of rotation of the recording medium.
According to the invention, the positioning means has spring elements and damper elements, which are arranged such that they are distributed uniformly over the circumference of the unbalance compensation means. This has the advantage that automatic centring of the recording medium relative to its axis of rotation is enabled as a result of this. Spring and damper forces cancel one another out by virtue of the uniformly distributed arrangement, and forces occurring in the event of an unbalance act on the spring and damper elements in such a way that the centre of mass of the recording medium is displaced towards the axis of rotation. This is carried out at a relatively low speed of rotation which is matched to the spring and damper forces or properties. The self-centred position of the recording medium is subsequently fixed and maintained.
According to the invention, the centrifugal force generation means has a mass element, which can be moved during operation. This has the advantage that the centrifugal force can be altered in a simple manner by alteration of the position of the mass element. In this case, the mass element is advantageously arranged on a rotating part and in a manner such that it can move with respect to this part, with the result that a displacement of the mass element is accompanied by an alteration of the unbalance. The invention provides for the use of one or more mass elements of this type. A single mass element is advantageously designed such that it can be displaced both radially and in the angular direction with respect to the rotation of the rotating part. The use of two mass elements has the advantage that they need be arranged such that they can be displaced in each case only in one dimension, that is to say radially or in the angular direction, in order to be able to compensate for the unbalance. The use of a larger number of mass elements, for example three, four or more, leads to more uniform mass distribution also in the direction of the axis of rotation. The higher symmetry that is obtained for these and even higher numbers such as, for example, six, eight, etc., contributes to reducing the wear and to simplifying production of the device.
The invention provides for two mass elements to be arranged such that they can move about the axis of rotation of the recording medium. This has the advantage that a change in the angular position of the mass elements is easily possible by virtue of the arrangement allowing movement about the axis of rotation. Since two mass elements are involved, the radial component of the mass distribution can also be set in a simple manner by a symmetrical change in the angular position of these mass elements. The mass elements advantageously have essentially the shape of a segment of a circle or segment of an annulus, in particular the shape of a semicircle or of half an annulus. If there are more than two mass elements, provision is made for correspondingly smaller segments of a circle which together produce a full circular disc, the consequence of this being the most uniform mass distribution possible. The movable securing of the mass elements should be designed to be as compact as possible in order to disrupt the mass distribution as little as possible. Segments of an annulus have the advantage that a greater mass accumulation is present radially on the outside, which, given an identical additional mass, enables greater effectiveness than in the case of radially uniform mass distribution. The axis of rotation is generally identical to that of the drive motor. The mass elements are advantageously arranged in proximity to the recording medium in order to compensate for the unbalance as close as possible to its source, and consequently to minimize mechanical stresses on the spindle and the bearings thereof, and also to prevent the propagation of vibration on device or drive motor to the greatest possible extent.
A further refinement of the invention provides for a plurality of small mass elements to be used which can be placed along a circumference or a radius of the centrifugal force generation means. This has the advantage that a larger number of mass elements can easily be metered and a high outlay in terms of mechanical holding is unnecessary, as a result of which the centrifugal force generation means can be designed in a space-saving manner. The mass elements can advantageously be placed on a circumference which, in the radial direction, is relatively far removed from the centre, since, at that location, their influence is relatively large even when the total mass is relatively small. In this case, the mass elements are advantageously held by the centripetal force, which is not present without rotation of the recording medium, in which case, however, unbalance compensation is not necessary either.
Instead of a circumference or a radius of the centrifugal force generation means, it is likewise possible to use the circumference or the radius generally of a rotating part, without leaving the scope of the present invention. The mass elements are advantageously designed as fine- or coarse-grained powder arranged, for example, in a closed container, in order to avoid any loss, in air, a specific other gas, at excess pressure or negative pressure, in a liquid or the like. The individual particles are advantageously of essentially spherical design so that they can be packed as densely as possible. It is advantageous, however, for them to have a flattened or rough surface in order to increase the reciprocal friction and, consequently, to hold a position which, once assumed, is classified as optimal.
The invention furthermore provides an adhesion element or a holding element to be arranged on the circumference and/or on the radius of the centrifugal force generation means. This has the advantage that, in addition to the centripetal force, a holding force or adhesion force is exerted on the mass elements, as a result of which the latter are held in their set position even with a reduced rotational speed. This solution is advantageous particularly when the rotary movement of the recording medium is stopped without the latter being removed from the device. In the event of subsequent, renewed operation, the unbalance compensation is then still preserved and it is possible to go over to interference-free playback operation more rapidly. The adhesion element is, for example, an adhering surface coating, for example an adhesive layer, a layer of electrostatic charge, a magnetized layer in the event of using magnetizable particles as mass elements, or another suitable adhesion element. The holding element is designed for example as a rough surface, as a surface like a bed of nails, or as a differently configured surface, in which the mass elements are fixedly suspended or are caught. Cavities with openings arranged in the direction of rotation are advantageously provided as the holding elements. This has the advantage that the mass elements are received and held therein. In order to neutralize the mass distribution that has been set, acceleration in the opposite direction is provided for example, as a result of which the mass elements are removed from the cavities.
According to the invention, the unbalance compensation means has a control means, which essentially follows the rotary movement of the unbalance compensation means. This has the advantage that the unbalance compensation means and the control means concomitantly rotating with the latter are at rest relative to one another, thereby making it unnecessary to transmit for example control information, energy, force or mutual influencing from stationary to rotating parts or elements. The mechanical and electrical outlay are thus reduced, as, too, is the power loss.
According to the invention, the control means is a lever element. This has the advantage that the control means is of mechanical design, does not require the supply of electrical energy and is simple to realize. Preferably, a plurality of lever elements, in particular ones of identical design, are used, one or else a plurality of lever elements being provided for each mass element.
According to the invention, the lever element has a point of action on a rotating part, a further point of action on a stationary part and also a point of action on a mass element. This has the advantage that point of action and lever element are arranged and designed in such a way that relative displacements, caused by the unbalance, of the points of action on the stationary part and on the rotating part initiate leverage which effects a displacement of the mass element in the opposite displacement direction to that caused by the unbalance.
Another aspect of the invention provides for the unbalance compensation means to have a control means which is arranged such that it is essentially stationary with respect to the device. This has the advantage that a control means arranged fixed with respect to the housing reduces the number of parts arranged such that they rotate and, consequently, the space requirement thereof. A control means arranged fixed with respect to the housing has the advantage, moreover, that supply lines e.g. for the purpose of control, power supply, etc., from the housing are possible without difficulty on account of the arrangement fixed with respect to the housing. Furthermore access to an actuating means which is arranged fixed with respect to the housing is possible without difficulty.
According to the invention, the stationary control means is a braking means, which influences the angular position and/or the radial position of the mass element. This has the advantage that the control is effected by a stationary braking means, and information and energy transmission can be realized in a simple manner. The braking means is advantageously an electromagnetic coil which moves a brake lever into one or two braking positions in which the mass element is braked. For example, the angular position of second mass elements is influenced, thereby enabling good unbalance compensation by means of a small number of components.
According to the invention, the braking means influences a positioning gear mechanism with rotating elements which is part of the unbalance compensation means. This has the advantage that the elements of the positioning gear mechanism are braked by the braking means and a gearing movement is thereby initiated. In this case, with a suitable design of the positioning gear mechanism, a single mass element is positioned in the radial direction and in the direction of rotation.
The invention furthermore provides for the braking means to be part of an engagement means for the recording medium in disc form. This has the advantage that a component which is present in any case is used for the purpose of unbalance compensation in a phase in which it is inactive in any case. The part of the engagement means is advantageously a lever by which another element, the so-called puck, is moved towards the recording medium or away from the latter. In this case, the unbalance compensation means is advantageously integrated in the engagement means. This has the advantage that the unbalance compensation means engages from the other side of the recording medium compared with the drive motor, and this means that on the drive motor side, it is not necessary to make any modifications to a device whose construction may have already been completed, and, nevertheless, the unbalance compensation means can be integrated since structural space for arranging the unbalance compensation means is more likely to be available on the side remote from the motor.
According to the invention, the control means has a long-range-force-generating element. This has the advantage that direct mechanical contact between control means and mass element or other rotating parts of the unbalance compensation means is unnecessary, thereby obtaining a reduction in friction losses. The long-range force that is provided is, for example, a magnetic force, generated by an electromagnetic, for example, an electrostatic force or another force transmitted without direct contact. According to the invention, the mass element is a magnetizable mass element and the long-range-force-generating element is a magnet. This has the advantage that magnetizable mass elements, for example iron particles, are inexpensive materials which are simple to manipulate. Magnets, in particular electromagnets, are likewise inexpensive to produce and, as mass-produced articles, have well-known properties. The magnetizable mass elements are positionally displaced by means of the magnet; for example, when iron particles are used, they are attracted by means of the electromagnet, gathered and, with the drive motor rotating, released at an angular position which has been determined as suitable. They are then pressed by the centrifugal force against an outer wall to which, for their part, they pass on the centrifugal force. The magnetizable mass element that is provided may be either an individual mass element or a small number of individual mass elements, or else a large number of mass elements, for example pulverulent mass elements. A magnetic fluid can likewise advantageously be used in this case.
The electromagnet is advantageously arranged in such a way that the force acts essentially in the radial direction, which enables a flat design of the centrifugal force generation means. A compact design in the radial direction is obtained when the electromagnet is arranged above or below the plane of the centrifugal force generation means, that is to say when the force acts essentially in the axial direction. A single electromagnet serves to release mass elements if appropriate in a metered manner or at various locations. Two electromagnets are provided in order to release mass elements at different locations so that optimum mass compensation, for example in accordance with two emplaceable mass elements, is consequently obtained. The arrangement of three or more magnets which are advantageously of smaller design and are arranged with higher symmetry also lies within the scope of the invention.
According to the invention, the unbalance compensation means is an additional force generation means, which is advantageously a long-range force generation means. This has the advantage of a lower mechanical outlay and, consequently, a reduced susceptibility to interference, since a movable mass element is not necessary and the centrifugal force is generated in a different way.
According to the invention, the long-range force generation means is a magnetic field generation means. This has the advantage that a magnetic force is relatively simple to generate, and that it has no, or only slight, interfering influences on other parts of the device. It is advantageous for a plurality of electromagnets to be arranged in a stationary manner, the said electromagnets exerting a force of attraction on a magnetizable, rotating element. In this case, at least three electromagnets, but advantageously a larger number thereof, are arranged such that they are distributed uniformly over the circumference. They are driven in such a way that a circulating magnetic field is produced which circulates at the rotation frequency of the rotating element and, consequently, exerts a force having a constant direction with respect to this rotating element. The field is generated in such a way that this force has a magnitude and direction suitable for compensating for the unbalance. Another advantageous refinement consists in equipping the rotating element with one or more electromagnets and arranging permanent magnets on the circumference in a stationary manner, all of which permanent magnets have their north poles directed radially inwards, for example. This has the advantage that the rotation frequency of the magnetic field generated always correctly corresponds to that of the recording medium and, consequently, specific regulation is not necessary for this. The electromagnets are advantageously supplied with energy inductively.
According to the invention, the magnetic field generation means is integrated in the drive motor. This has the advantage that no additional structural space is necessary for the magnetic field generation means in the device, and that this function is in any case obtained in the drive motor designed as an electric motor. Given an electronically commutated motor, a centrifugal force control signal is accordingly superposed on the normal signal of the solenoids, with the result that the circulating force which compensates for the unbalance is additionally superposed on the circulating travelling field. Instead of the magnetic field generation means, it likewise lies within the scope of the invention to integrate a general long-range force generation means in the drive motor.
The invention provides for a sensor and an evaluation means to be present in the device. This has the advantage that the requisite centrifugal force is optimally determined and set in terms of magnitude and direction. A slow run-up to the optimum value or rapid overshooting beyond this optimum value need not be feared, therefore. Consequently, the optimum operating state is reached rapidly and reliably. The evaluation means evaluates the sensor signal and determines the tractive force suitable for unbalance compensation.
According to the invention, the sensor is a vibration sensor. This has the advantage that the undesirable property caused by the unbalance is measured directly. In this way, the unbalance is compensated such that minimum vibration is achieved. This applies, when a vibration sensor is used, even when other influences are superposed on the unbalance and, therefore, optimum unbalance compensation possibly does not correspond to optimum vibration damping.
According to the invention, the unbalance compensation means has a sensor element, an evaluation means and a centrifugal force generation means and/or a positioning means, which are all arranged on a rotating part of the device. This has the advantage that the unbalance compensation means is arranged in a particularly space-saving manner, since an information flow between a rotating part and a non-rotating part is not necessary.
The said elements are advantageously designed as micromechanical and microelectronic elements, so-called mechatronic elements. Accordingly, sensor element, evaluation means, centrifugal force generation means and/or positioning means are all arranged on a single mechatronic support element. The sensor is advantageously designed as a rotation sensor. The positioning means and/or the centrifugal force generation means are/is designed for example as micropump and microvalves interacting therewith, which displaces hydraulic mass elements and/or positions the recording medium. Since, in some instances, only relatively small masses are required for the compensation, micromechanical elements can be used practically in this case. Energy is advantageously supplied by way of the electrodynamic effect or coupling-in of radiation.
An inventive method for setting a variable centrifugal force of a centrifugal force generation means has the steps specified in the independent method claim.
These steps have the advantage that a simple yet reliable method is realized in this way for the purpose of setting a centrifugal force and hence compensating for the unbalance which is caused in a device for reading from and/or writing to recording media in disc form as a result of non-uniform mass distribution of the recording medium or inaccurate positioning thereof in the device. In this case, the comparison of the difference between present value and stored value is preferably effected in terms of magnitude or by way of defined upper and lower threshold values. In general, the change in the moment of inertia is preferably effected by changing the radius, but may likewise advantageously be obtained by changing the mass of the mass element. A step d), addition of a mass element, is advantageously carried out between steps c) and e) of he method. The addition may consist in the actual insertion of a mass element from the outside into the centrifugal force generation means; however, addition may likewise be understood to mean that a mass element is moved from a starting position to a different suitable position.
Further advantages and refinements of the invention may be gathered from the following description of advantageous exemplary embodiments.